A New Route to Chelating Bis(aryloxide) Ligands and Their Applications to Tantalum and Titanium Organometallic Compounds

Article abstract of DOI:10.1021/ic030300s

A new route to sterically tuned, chelating bis(aryloxide) ligands is ′described and demonstrated by the synthesis of 2,2-ethylenebis(6-isopropylphenol) (1, H₂BIPP) and transition metal complexes of its dianion. The utility of these ligands in titanium and tantalum organometallic chemistry is shown in the alkylation of (BIPP)TiCl₂ (7) to form (BIPP)TiMe₂ (8) and (BIPP)Ti(CH₂Ph) ₂ (9) and in the alkylation of (BIPP)TaCl₃ (10) and its base adducts to form (BIPP)TaMe₃ (14) and (BIPP)Ta(CH ₂Ph)₃ (13). Structural comparisons of the chelating 2,2′-ethylenebis(6-isopropylphenoxide) (BIPP) ligand with its analogous, nonchelating bis(2,6-dialkylaryloxide) ligand set are examined in the X-ray diffraction studies of (BIPP)TaCl₃(THF)·THF (11·THF) and (BIPP)Ta(CH₂C₆H₅)₃ (13).

Full text of DOI:10.1021/ic030300s

Inorg. Chem. 2004, 43, 716−724
A New Route to Chelating Bis(aryloxide) Ligands and Their Applications
to Tantalum and Titanium Organometallic Compounds†
,§
Jeffrey W. Anthis,‡ Igor Filippov, and David E. Wigley*
Department of Chemistry, The UniVersity of Arizona, Tucson, Arizona 85721
Received October 20, 2003
A new route to sterically tuned, chelating bis(aryloxide) ligands is described and demonstrated by the synthesis of
2,2′-ethylenebis(6-isopropylphenol) (1, H BIPP) and transition metal complexes of its dianion. The utility of these
2
ligands in titanium and tantalum organometallic chemistry is shown in the alkylation of (BIPP)TiCl2 (7) to form
(BIPP)TiMe2 (8) and (BIPP)Ti(CH Ph)2 (9) and in the alkylation of (BIPP)TaCl3 (10) and its base adducts to form
2
(BIPP)TaMe3 (14) and (BIPP)Ta(CH Ph)3 (13). Structural comparisons of the chelating 2,2′-ethylenebis(6-
2
isopropylphenoxide) (BIPP) ligand with its analogous, nonchelating bis(2,6-dialkylaryloxide) ligand set are examined
in the X-ray diffraction studies of (BIPP)TaCl3(THF)‚THF (11‚THF) and (BIPP)Ta(CH C H ) (13).
2
6 5 3
Introduction
uncommon upon reducing d0 group 5 transition metal
complexes with ancillary 2,6-dialkylaryloxide ligands.
In our preparative approach to certain d2 niobium and
tantalum bis(2,6-diisopropylaryloxide) complexes, we also
encountered cyclometalation reactivity of the isopropyl
groups on these ligands and thus set out to design chelating
ligands with steric and electronic properties similar to those
of the bis(2,6-diisopropylaryloxide) ligand set but with
potentially lower cyclometalation reactivity. In this report,
we describe the synthesis of an ethylene-linked bis(aryloxide)
ligand and the preparation and properties of some of its
complexes of tantalum and titanium.
Despite the abundance of aryloxide ligands throughout
transition metal chemistry,1 there are relatively few examples
of chelating bis(aryloxide) ligands and even fewer instances
of chelating bis(aryloxide) ligands with ethylene-bridged aryl
rings. Okuda and co-workers have demonstrated that ethyl-
ene-bridged 2,2′-ethylenebis(6-tert-butyl-4-methylphenol) (eb-
mpH2) is useful in the polymerization of ethylene when
bound to titanium.2 In addition to its potential general utility
as a ligand for Lewis acid catalysts, we envision ethylene-
bridged bis(aryloxide) ligands as playing an important role
in circumventing the problems associated with cyclometa-
lation of certain 2,6-dialkylaryloxide ligands.3-8 Cyclo-
metalation of an ortho-alkyl group of such ligands is not
Results and Discussion
Synthesis of 2,2′-Ethylenebis(6-isopropylphenol) (1,
H2BIPP). The synthesis of 2,2′-ethylenebis(6-isopropylphen-
ol), abbreviated H2BIPP, is summarized in Scheme 1. We
envisioned a synthetic approach that would allow for a
sterically tunable and inexpensive ethylene-linked bis-
(aryloxide) ligand. Accordingly, this synthesis was ac-
complished starting with a 2-substituted phenol, which allows
the preparation of chelating analogues of the analogous bis-
(2,6-dialklaryloxide) ligand set. This approach was developed
using the isopropyl-substituted material, 2-isopropylphenol,
but other 2-alkylphenols can be used (e.g. 2-tert-butylphenol)
to afford a variety of substituted bis(phenol) ligands.
The alcohol was protected as a methoxy group via
deprotonation with potassium, followed by quenching with
* Corresponding author. E-mail: dwigley@kilpatrickstockton.com.
† In loving memory of W.R.A.
‡ Present address: Epichem, Inc., 1429 Hilldale Avenue, Haverhill, MA
01832.
§ Present address: Kilpatrick Stockton LLP, 1100 Peachtree Street, Suite
2800, Atlanta, GA 30309-4530.
(1) For a comprehensive review of transition metal aryloxide chemistry,
see: Bradley, D. C.; Mehrotra, R. C.; Rothwell, I. P.; Singh, A. Alkoxo
and Aryloxo DeriVatiVes of Metals; Academic Press: San Diego, CA,
2001.
(2) Fokken, S.; Spaniol, T. P.; Okuda, J.; Sernetz, F. G.; Muelhaupt, R.
Organometallics 1997, 16, 4240-4242.
(3) Mulford, D. R.; Clark, J. R.; Schweiger, S. W.; Fanwick, P. E.;
Rothwell, I. P. Organometallics 1999, 18, 4448-4458.
(4) Steffey, B. D.; Chamberlain, L. R.; Chesnut, R. W.; Chebi, D. E.;
Fanwick, P. E.; Rothwell, I. P. Organometallics 1989, 8, 1419-1423.
(5) Chamberlain, L. R.; Kerschner, J. L.; Rothwell, A. P.; Rothwell, I.
P.; Huffman, J. C. J. Am. Chem. Soc. 1987, 109, 6471-6478.
(6) Chesnut, R. W.; Steffy, B. D.; Rothwell, I. P. Polyhedron 1988, 9,
753-756.
(7) Rabinovich, D.; Zelman, R.; Parkin, G. J. Am. Chem. Soc. 1992, 114,
4611-4621.
(8) Rabinovich, D.; Zelman, R.; Parkin, G. J. Am. Chem. Soc. 1990, 112,
9632-9633.
716 Inorganic Chemistry, Vol. 43, No. 2, 2004
10.1021/ic030300s CCC: $27.50 © 2004 American Chemical Society
Published on Web 12/20/2003

Chelating Bis(aryloxide) Ligands
Scheme 1
Scheme 2
methyl iodide to provide 2-isopropylanisol (2) in 87% yield.
The methoxy protecting group was used because of its robust
nature, and the final product allows for the harsh cleaving
conditions required to remove it. The ortho-lithiated product
(3-isopropyl-2-methoxyphenyl)lithium‚0.5TMEDA (3) was
synthesized from 2 using n-butyllithium under standard
conditions.9,10 Compound 3 was isolated as a white powder
and was stable indefinitely at room temperature under a
nitrogen atmosphere. The isolation of 3 was not necessary
for the effective synthesis of H2BIPP (1), as 3 could be
converted to the benzyl alcohol 4 in situ. However, the utility
of 3 for other ligand preparations and its thermal stability
resulted in its isolation as the standard synthetic procedure.
The benzyl alcohol 4 was synthesized from 3 upon its
reaction with paraformaldehyde, following an acid workup,
which afforded 2-(hydroxymethyl)-6-isopropylanisole (4) in
high (81%) yield. Bromination of the benzyl alcohol with
bromine/triphenylphosphine was effected under standard
conditions to provide 2-(bromomethyl)-6-isopropylanisole (5)
in 86% yield.11 We found that the workup of 5 was best
carried out while being stirred rapidly with a mechanical
stirrer to minimize the size of the triphenylphosphine oxide
clumps that precipitated during this procedure. 2,2′-Ethyl-
enebis(6-isopropylanisole) (Me2BIPP, 6) was synthesized
through the low-temperature homocoupling of 5 with n-
butyllithium. Compound 6 was then deprotected using boron
tribromide, followed by an acidic workup, to yield 2,2′-
ethylenebis(6-isopropylphenol) (1, H2BIPP) in an overall
yield of 44.3% for the six-step synthesis.
both tantalum and titanium compounds of this ligand from
their respective d0 halides. Scheme 2 outlines reactions to
form the titanium BIPP complexes. The titanium complex
(BIPP)TiCl2 (7) was synthesized by the method of Okuda
and co-workers,2 by adding a solution of H2BIPP (1) in
pentane to a concentrated solution of titanium tetrachloride
in pentane at room temperature. The product precipitated
from the reaction solution as a dark red solid within seconds
of adding the ligand. Filtration of the precipitate afforded
analytically pure product with no further purification re-
quired. Compound 7 was soluble in several organic solvents
including pentane, from which crystals could be grown.
Reacting 7 with the methyl and benzyl Grignards afforded
(BIPP)TiMe2 (8) and (BIPP)Ti(CH2C6H5)2 (9), respectively,
in moderate yields as highly soluble red to orange
solids.
Transition Metal-BIPP Complexes. To examine the
chelating bis(aryloxide) compound and compare it structur-
ally with the analogous bis(2,6-diisopropylphenoxide) ligand
set which has shown considerable utility,12-19 we prepared
(14) Weller, K. J.; Fox, P. A.; Gray, S. D.; Wigley, D. E. Polyhedron 1997,
16, 3139.
(9) Filippov, I. Metal-Mediated Hydrodenitrogenation Catalysis: Design-
ing New Models; Ph.D. Dissertation; University of Arizona: Tucson,
AZ, 1998; p 218.
(10) Graybill, B. M.; Shirley, D. A. J. Org. Chem. 1966, 31, 1221-1224.
(11) Wiley, G. A.; Hershkowitz, R. L.; Rein, B. M.; Chung, B. C. J. Am.
Chem. Soc. 1964, 86, 964-965.
(12) Fox, P. A.; Bruck, M. A.; Gray, S. D.; Gruhn, N. E.; Grittini, C.;
Wigley, D. E. Organometallics 1998, 17, 2120.
(15) Weller, K. J.; Filippov, I.; Briggs, P. M.; Wigley, D. E. J. Organomet.
Chem. 1997, 528, 225.
(16) Weller, K. J.; Gray, S. D.; Briggs, P. M.; Wigley, D. E. Organome-
tallics 1995, 14, 5588.
(17) Gray, S. D.; Weller, K. J.; Bruck, M. A.; Briggs, P. M.; Wigley, D.
E. J. Am. Chem. Soc. 1995, 117, 10678.
(18) Allen, K. D.; Bruck, M. A.; Gray, S. D.; Kingsborough, R. P.; Smith,
D. P.; Weller, K. J.; Wigley, D. E. Polyhedron 1995, 14, 3315.
(19) Smith, D. P.; Strickler, J. R.; Gray, S. D.; Bruck, M. A.; Holmes, R.
S.; Wigley, D. E. Organometallics 1992, 11, 1275.
(13) Weller, K. J.; Filippov, I.; Briggs, P. M.; Wigley, D. E. Organome-
tallics 1998, 17, 322.
Inorganic Chemistry, Vol. 43, No. 2, 2004 717

Anthis et al.
Scheme 3
All three titanium compounds, 7-9, were thermally stable
days reaction time revealed a mixture of (BIPP)TaCl3 (10)
and another product (A). Subsequent examination of the same
reaction mixture revealed the slow conversion of A to 10 as
the reaction proceeded to completion. Compound A is
characterized by a simple 1H NMR spectrum, similar to that
of 10. Although A was not isolated or fully characterized,
its 1H NMR and reactivity data suggest its possible formula-
tion as the bis(BIPP) complex (BIPP)2TaCl, which is capable
of subsequent reaction with TaCl5 to afford 2 equiv of
(BIPP)TaCl3 (10). However, other formuations of A are
possible, including a monomer/µ-Cl dimer relationship
between 10 and A.
The proton NMR of compound (BIPP)TaCl3(THF) (11)
in THF-d8 showed two sharp septet resonances indicating
inequivalent isopropyl methine protons, consistent with the
two 13C resonances observed for the corresponding carbon
atoms. These NMR data suggest that the coordinated THF
molecule is bound trans to one of the BIPP oxygen donors,
and cis to the other, thereby rendering the ends of the BIPP
ligand inequivalent. As described below, the X-ray structural
study of this adduct reveals a mer isomer of 11 in the solid
state, consistent with this observed solution structure.
The organometallic compounds (BIPP)Ta(CH2C6H5)3 (13)
and (BIPP)TaMe3 (14) were synthesized by reacting the
appropriate Grignard reagent with (BIPP)TaCl3 in diethyl
ether. The highly soluble benzyl derivative (BIPP)Ta-
(CH2C6H5)3 (13) was isolated as a crystalline orange solid,
which was thermally stable for at least several months at
room temperature under nitrogen atmosphere. In contrast,
while the methyl compound (BIPP)TaMe3 (14) was observ-
able by 1H and 13C NMR spectroscopy and could be isolated
as a mixture, attempts to isolate this compound in pure form
were unsuccessful. Attempts to isolate partially substituted
compounds (BIPP)Ta(CH2C6H5)nCl3-n and (BIPP)TaMenCl3-n
using a lower mole ratio of Grignard to metal halide typically
resulted in intractable mixtures.
for at least several months at room temperature under a
1
nitrogen atmosphere. The H and 13C NMR spectra of all
three compounds showed only single, sharp resonances
corresponding to the ethylene backbone of the BIPP ligand.
The methyl and benzyl groups of 8 and 9 were also observed
1
to be equivalent by H and 13C NMR spectroscopy.
Scheme 3 outlines reactions to form the tantalum BIPP
complexes. When a solution of H2BIPP in THF or Et2O was
added to a solution of TaCl5 in the corresponding THF or
Et2O solvent, the adducts (BIPP)TaCl3L could be isolated
as a bright yellow powders upon precipitation with pentane
(L ) THF (11) or Et2O (12)). Solid samples of both products
isolated in this manner contained nonstoichiometric amounts
of coordinating solvent which could be substantially removed
under high vacuum over an extended period of time, such
that the formulation of 11 and 12 approached (BIPP)TaCl3L.
Compound 11 was poorly soluble in most solvents except
THF. Pure crystals of 11 grown from THF at -35 °C and
of 12 grown from Et2O at -35 °C contained a single
molecule of lattice solvent, forming (BIPP)TaCl3(THF)‚THF
(11‚THF) and (BIPP)TaCl3(OEt2)‚OEt2 (12‚OEt2), respec-
tively.
Base-free (BIPP)TaCl3 (10) was synthesized in 85% yield
by the reaction of H2BIPP and TaCl5 in a benzene slurry,
over a 4 day period at room temperature. Shorter reactions
times yielded an intermediate product (A), which over time
converted to 10. When the synthesis of base-free (BIPP)-
TaCl3 was attempted at elevated temperatures, only intrac-
table decomposition products were obtained.
An examination of the H2BIPP and TaCl5 reaction mixture
in benzene revealed the following. When a benzene solution
of H2BIPP was first added to a benzene slurry of TaCl5, the
solution rapidly turned dark yellow-brown. Although (BIPP)-
TaCl3 (10) subsequently formed in high yield from this
solution, examining the reaction mixture after less than 4
718 Inorganic Chemistry, Vol. 43, No. 2, 2004

Chelating Bis(aryloxide) Ligands
Table 1. Details of the X-ray Diffraction Studies for (BIPP)TaCl3(THF)‚THF (11‚THF) and (BIPP)Ta(CH2C6H5)3 (13)
param
11‚THF
13
Crystal Parameters
molecular formula
Mr
C28H40Cl3O4Ta
727.90
C41H45O2Ta
750.72
F(000)
1456
1520
cryst color
space group
unit cell vol, Å3
a, Å
b, Å
c, Å
yellow
orange
P21/c (No. 14)
3039.5(4)
10.5486(9)
17.1174(14)
16.9328(15)
96.215(4)
4
P21/c (No. 14)
3421.8(2)
10.2826(3)
16.6334(6)
20.0078(7)
90.7020(10)
4
â, deg
Z
D(calcd), g cm-3
cryst dimens, mm
Ω width, deg
exposure time, s
abs coeff, cm-1
data collcn temp, K
1.591
1.457
0.33 × 0.20 × 0.15
0.2 × 0.3 × 0.4
0.3
0.3
10
39.10
170(2)
10
32.46
443(2)
Data Collection
diffractometer
monochromator
Bruker SMART 1000 CCD
graphite
Bruker SMART 1000 CCD
graphite
Mo KR radiation λ, Å
0.710 73
2-60
0.710 73
2-60
2θ range, deg
tot. no. of refclns measd
corrs
78 412 reflections (26 397 unique)
empirical abs and decay using SADABS
(SHELDRICK)
24 443 reflections (8502 unique)
empirical abs and decay using SADABS
(SHELDRICK)
Solution and Refinement
solution
direct methods
direct methods
refinement
full-matrix least squares
full-matrix least squares
minimization function
reflcns used in refinement; I > 2σ(I)
param refined
Σw(|Fo| - |Fc|)2
Σw(|Fo| - |Fc|)2
8175 (69%)
308
6406 (75%)
405
R ()∑||Fo| - |Fc||/∑|Fo|) (I > 2σ(I))
R1 ) 0.0698
R1 ) 0.0259
R
w ()[∑w(|Fo| - |Fc|)2/∑w(Fo)2]1/2) (I > 2σ(I))
wR2 ) 0.1788
wR2 ) 0.0462
convergence, largest shift
∆/σ(max), e/Å3
∆/σ(min), e/Å3
software
0.005σ
2.535
-1.656
0.003σ
1.074
-0.669
SHELXS in Bruker SHELXTL (version 5.0)20
SHELXS in Bruker SHELXTL (version 5.0)20
Table 2. Selected Bond Distances (Å), Bond Angles (deg), and
Torsion Angles (deg) in (BIPP)TaCl3(THF)‚THF (11‚THF)
The 1H and 13C NMR spectra of tantalum BIPP compounds
11-14 all exhibited single, sometimes broad, resonances
corresponding to the ethylene backbone of the BIPP ligand.
This observation likely reflects the fluxionality of the five-
coordinate benzyl (13) and methyl (14) compounds and the
lability of the ether base in compounds 11 and 12.
X-ray Crystallographic Studies of BIPP Compounds.
Yellow, block-shaped crystals of (BIPP)TaCl3(THF)‚THF
(11‚THF) and orange, block crystals of (BIPP)TaBn3 (13)
suitable for X-ray structural studies were grown at -35 °C
from THF and Et2O solutions, respectively. (BIPP)TaCl3-
(THF)‚THF (11‚THF) grew as a pseudomirrorhedral twin
and was solved accordingly.20 A summary of the crystal data
and structural analysis is given in Table 1. Relevant bond
distances, bond angles, and torsion angles for 11‚THF are
provided in Table 2, and those for 13 are provided in Table
3. Figures 1 and 2 present ORTEP drawings (50% thermal
probability ellipsoids) of (BIPP)TaCl3(THF)‚THF (11‚THF)
and (BIPP)TaBn3 (13), respectively.
Bond Distances
Ta(1)-O(1)
Ta(1)-O(2)
Ta(1)-O(3)
1.8405(56)
1.8618(57)
2.192(6)
Ta(1)-Cl(1)
Ta(1)-Cl(2)
Ta(1)-Cl(3)
2.363(2)
2.371(3)
2.388(3)
Bond Angles
99.86(25) O(1)-Ta(1)-Cl(3) 166.88(19)
O(1)-Ta(1)-O(2)
Ta(1)-O(1)-C(1)
Ta(1)-O(2)-C(11)
C(6)-C(10)-C(20)
171.05(59) O(1)-Ta(1)-O(3)
170.97(59) O(2)-Ta(1)-Cl(1)
84.6(2)
91.11(19)
96.36(19)
93.19(19)
174.6(2)
111.1(8)
O(2)-Ta(1)-Cl(2)
O(2)-Ta(1)-Cl(3)
O(2)-Ta(1)-O(3)
C(16)-C(20)-C(10) 112.9(8)
O(1)-Ta(1)-Cl(1)
O(1)-Ta(1)-Cl(2)
92.4(2)
89.6(2)
Torsion Angles
C(6)-C(10)-C(20)-C(16) 161.5(9) O(1)-Ta(1)-O(2)-C(11) 27.4(4)
Ta(1)-O(1)-C(1)-C(6) 33(4) O(2)-Ta(1)-O(1)-C(1) 9(4)
Ta(1)-O(2)-C(11)-C(16) 40(4)
below the O(1)-Cl(1)-Cl(2)-Cl(3) plane. Table 2 reveals
that the O(1)-Ta(1)-O(2) bite angle formed by the BIPP
ligand is 99.86(25)°, which is only slightly larger than an
analogous compound without linked aryloxide ligation,
(DIPP)2TaCl3(pyridine) (DIPP ) 2,6-diisopropylphenoxide),
which displays an O-Ta-O bond angle of 95.0(2)°.21 The
Ta(1)-O(1)-C(1) and Ta(1)-O(2)-C(11) angles are 171.05-
Molecular Structure of (BIPP)TaCl3(THF)‚THF (11‚
THF). The molecular geometry of 11‚THF shown in Figure
1 can be described as a distorted octahedral structure, having
a mer geometry, with the tantalum atom situated slightly
(20) Sheldrik, G. M. In SHELLXTL, 5.1 ed.; Sheldrik, G. M., Ed.; Bruker
(21) Clark, J. R.; Pulvirenti, A. L.; Fanwick, P. E.; Sigalas, M.; Eisenstein,
AXS: Madison, WI, 1997.
O.; Rothwell, I. P. Inorg. Chem. 1997, 36, 3623-3631.
Inorganic Chemistry, Vol. 43, No. 2, 2004 719

Anthis et al.
Figure 1. ORTEP drawing (BIPP)TaCl3(THF)‚THF (11‚THF) with 50%
thermal ellipsoids. The lattice THF molecule has been removed for clarity.
Table 3. Selected Bond Distances (Å), Bond Angles (deg), and
Torsion Angles (deg) in (BIPP)Ta(CH2C6H5)3 (13)
Bond Distances
Ta(1)-O(1)
1.8375(18)
Ta(1)-O(2)
1.8731(17)
Bond Angles
O(1)-Ta(1)-O(2)
Ta(1)-O(1)-C(1)
Ta(1)-O(2)-C(2)
117.20(8) O(1)-Ta(1)-C(35)
159.49(17) O(2)-Ta(1)-C(21)
159.24(18) O(2)-Ta(1)-C(28)
107.33(10)
139.80(9)
88.46(9)
C(6)-C(10)-C(20) 113.6(2)
C(16)-C(20)-C(10) 112.8(2)
O(2)-Ta(1)-C(35)
89.21(9)
Ta(1)-C(21)-C(22)ipso 119.6(7)
O(1)-Ta(1)-C(21) 102.98(9) Ta(1)-C(28)-C(29)ipso 105.91(18)
O(1)-Ta(1)-C(28) 107.77(10) Ta(1)-C(35)-C(36)ipso 107.95(17)
Torsion Angles
C(6)-C(10)-C(20)-C(16) 164.1(2) O(1)-Ta(1)-O(2)-C(11) 4.6(5)
Ta(1)-O(1)-C(1)-C(6)
17.9(7) O(2)-Ta(1)-O(1)-C(1) 1.7(5)
Ta(1)-O(2)-C(11)-C(16) 18.6(6)
(59) and 170.97(59)°, respectively, which, again, are similar
to the angles of 173.8(5) and 174.0(5)° of the analogous,
nonlinked or nonchelating bis(aryloxide) complex (DIPP)2-
TaCl3(pyridine). Thus, the apparent flexibility of the BIPP
ligand through its ethylene bridge allows the molecule to
attain a near-octahedral structure very similar to its non-
chelated analogue.
Figure 2. ORTEP drawings of (BIPP)Ta(CH2C6H5)3 (13) with 50%
thermal ellipsoids. In view A, the isopropyl groups have been removed for
clarity. View B looks down the pseudoaxis of the trigonal bipyramid normal
to the equatorial plane
Molecular Structure of (BIPP)TaBn3 (13). As shown
in Figure 2 and in Table 3, the structural properties of the
BIPP ligand in compound 13 are similar to those described
for 11‚THF above. The molecular structure of 13 can be
described as distorted trigonal bipyramidal in which Ta(1),
O(1), O(2), and C(21) comprise the equatorial plane, while
the benzyl groups containing C(28) and C(35) occupy the
axial positions. This structure differs significantly from the
analogous nonlinked bis(aryloxide) tris(benzyl) compound
reported by Rothwell and co-workers, (DMP)2Ta(CH2Ph)3
(DMP ) 2,6-dimethylphenoxide).22 While (DMP)2Ta(CH2-
Ph)3 is characterized by a trigonal bipyramidal geometry,
the aryloxide ligands occupy axial sites with the three benzyl
groups residing in the equatorial plane. The O(1)-Ta(1)-
O(1) angle created by the BIPP ligand in 13 is 117.20(8)°,
which is close to idealized trigonal bipyramidal geometry.
The equatorial benzyl group, however, is distorted somewhat
from an ideal TBP with O(1)-Ta(1)-C(21) and O(2)-Ta-
(1)-C(21) angles of 102.98(9) and 139.80(9)°, respectively.
This latter feature demonstrates the distortion toward the
square pyramidal geometry, in which the BIPP ligand
occupies the axial and one basal position, while the benzyl
ligands all occupy basal sites.
The Ta(1)-O(1)-C(1) and Ta(1)-O(2)-C(11) bond
angles of 159.49(17) and 159.24(18)° in 13 correspond to
Ta-O bond lengths of 1.8375(18) Å for Ta(1)-O(1) and
1.8731(17) Å for Ta(1)-O(2). These Ta-O-Cipso angles in
13 are consistent with the analogous nonlinked, bis(aryloxide)
complex (DMP)2Ta(CH2Ph)3, which exhibits by Ta-O-Cipso
angles of 158.9(4) and 150.6(4)°.
One striking feature of the axial benzyl ligands in 13 is
the rotational orientation of their Ta-CR-Cipso angles with
respect to the TBP equatorial plane, such that the phenyl
rings are situated above and below the rough plane formed
by the chelating BIPP ligand and tantalum center. This
feature may simply reflect the most efficient packing of the
axial ligands about the metal. Further, the Ta-CR-Cipso
angles of these axial benzyl ligands, 105.91(18)° for Ta-
(22) Chamberlain, L. R.; Rothwell, I. P.; Folting, K.; Huffman, J. C. J.
Chem. Soc., Dalton Trans. 1987, 155-162.
720 Inorganic Chemistry, Vol. 43, No. 2, 2004

Chelating Bis(aryloxide) Ligands
(1)-C(28)-C(29)ipso and 107.95(17)° for Ta(1)-C(35)-
C(36)ipso, stand in contast to the larger Ta(1)-C(21)-
C(22)ipso angle of 119.6(7)° for the equatorial benzyl. These
more acute axial Ta-CR-Cipso angles suggest an allylic
contribution to the benzyl ligand structure, though the similar
carbon-carbon bond lengths in the benzyl aryl might suggest
otherwise.
to a large extent through the wide range of accessible Ta-
O-Cipso angle.
Experimental Section
General Details. All experiments were performed under a
nitrogen atmosphere either by standard Schlenk techniques23 or in
a Vacuum Atmospheres HE-493 drybox at room temperature, unless
otherwise indicated. Solvents were distilled under N2 from an
appropriate drying agent and were transferred to the drybox without
exposure to air. 2-Isopropylphenol (1), TMEDA (redistilled, 99.5%),
triphenylphosphine, BBr3 (1 M in CH2Cl2), Br2, n-butyllithium (1.6
M in hexanes), CH3I (99.5%), and paraformaldehyde were pur-
chased from Aldrich (Milwaukee, WI). Reagents TMEDA, tri-
phenylphosphine, BBr3, Br2, n-butyllithium, and CH3I were used
as received, while 2-isopropylphenol (1) was dried over 4 Å
molecular sieves and distilled prior to use. Paraformaldehyde was
dried in vacuo for 4 h prior to use. Tantalum pentachloride (TaCl5)
was obtained form CERAC, Inc. (Milwaukee, WI), and used as
received. Titanium tetrachloride (TiCl4) was purchased from Aldrich
and used as received. All Grignard reagents were also purchased
from Aldrich and used as received. In all preparations, BIPP ) the
2,2′-ethylenebis(6-isopropylphenoxide) dianion.
Physical Measurements. 1H NMR and 13C NMR spectra were
recorded at probe temperature using either a Varian Unity 300
spectrometer or a Bruker AM-250 spectrometer in C6D6 or THF-
d8 solvent. Chemical shifts are referenced to the protio impurities
(δ 7.15, C6D6; δ 3.58, THF-d8) or solvent 13C resonances (δ 128.4,
C6D6; δ 67.6, THF-d8) and are reported downfield of Me4Si. Carbon
13C assignments were assisted by HETCOR and HMBC spectra
acquired at 30 °C without sample spinning. Microanalyses were
preformed by Desert Analytics, Tucson, AZ. Microanalytical
samples were routinely handled under nitrogen, and all samples
were combusted with WO3.
Preparations. 2-Isopropylanisole (2). In a typical experiment,
a large Schlenk tube equipped with a magnetic stir bar was charged
with 500 mL of THF and 28.53 g (0.729 mol) of potassium chunks.
The mixture was cooled in an ice bath and vigorously stirred, while
a solution of 99.99 g (0.734 mol) of isopropylphenol (1) in 100
mL of THF was slowly added. The resulting reaction mixture was
stirred for 2-3 h at 0 °C under a slow purge of N2, after which
time it was allowed to warm to room temperature and stirred for
an additional 3-4 h until all of the potassium had reacted. After
this time, the solution was again cooled to 0 °C in an ice bath, and
105.57 g (0.743 mol) of CH3I was added slowly. The resulting
mixture was stirred overnight at room temperature, over which time
a white solid precipitated. This slurry was extracted with water to
remove the potassium iodide that had formed during the reaction.
The aqueous layer was extracted with 50 mL of diethyl ether, and
this ether extract was combined with the THF layer. The combined
organic layers were washed with a saturated NaCl solution (2 ×
100 mL) and dried over anhydrous MgSO4, and the solvent was
removed in vacuo to afford a yellow liquid. Distillation of this liquid
from sodium at atmospheric pressure gave 83.31 g (0.555 mol, 87%)
of a clear, colorless liquid 2 with a boiling point of 190-192 °C.
1H NMR (C6D6): δ 7.20-6.55 (m, 4 H, Haryl), 3.50 (spt, 1 H,
CHMe2), 3.34 (OCH3), 1.24 (d, 6 H, CHMe2). 13C NMR (C6D6):
δ 157.15, 137.01, 126.86, 126.31, 120.97, 110.50, 54.78, 27.10,
22.91.
One measure of BIPP ligand structure is the C(6)-C(10)-
C(20)-C(16) torsion angle, which simply indicates the
orientation about the ethylene linker between the aryl rings.
The C(6)-C(10)-C(20)-C(16) torsion angle in 13 is
164.1(2)°, which drives the BIPP phenyl rings nearly
coplanar (dihedral angle 16.59(16)°), similar to its structure
in 11‚THF, where this torsion angle is 161.5(9)°.
Bond Length/Bond Angle Comparisons between Tan-
talum BIPP Complexes. Tables 2 and 3 allow a ready
comparison of bond angles and distances between (BIPP)-
TaCl3(THF)‚THF (11‚THF) and (BIPP)Ta(CH2Ph)3 (13).
Comparing the O(1)-Ta(1)-O(2) bite angles of 99.86(25)°
for 11‚THF and 117.20(8)° for 13, we see that although the
ligand is constrained to be cis, it is flexible enough to allow
for both octahedral and trigonal geometries. One obvious
difference between the two BIPP ligands that allows them
to form bite angles of this range is the flexibility of the Ta-
O-Cipso bond angles. The Ta-O(1)-C(1) and Ta-O(2)-
C(2) angles in 11‚THF are 171.05(59) and 170.97(59)°,
respectively, whereas the same angles in 13 are 159.49(17)
and 159.24(18)°.
Other more subtle but important differences between the
two compounds are the “chelate” Ta-O(1)-C(1)-C(6) and
Ta-O(2)-C(11)-C(16) torsion angles. The octahedral
compound 11‚THF has Ta-O(1)-C(1)-C(6) and Ta-
O(2)-C(11)-C(16) torsion angles of 33(4) and 40(4)°,
respectively, while the trigonal compound, 13, has angles
of 17.9(7) and 18.6(6)°. These data appear to correlate an
increasing BIPP bite angle with increasingly planar aryl rings,
which become increasingly necessary to accommodate a
larger bite angle. Thus, the more the Ta-O(1)-C(1)-C(6)
and Ta-O(2)-C(11)-C(16) angles approach 0°, the greater
the O-Ta-O angle that ligand must span as the aryl ring
planes approach coplanarity with the chlelate ring plane.
Conclusions
A new route to ethylene bis(aryloxide) ligands has been
developed. The new H2BIPP (1) ligand readily reacts with
the d0 chlorides of tantalum and titanium to form the
complexes (BIPP)TaCl3 and (BIPP)TiCl2, respectively. These
compounds react with Grignard reagents to afford the
corresponding alkyl complexes. In (BIPP)Ta(CH2Ph)3 (13),
the ethylene bridge constrains the aryloxide portions of the
BIPP ligand to reside in a TBP equatorial plane rather than
in the axial positions as observed in the unlinked analogue.
A structural comparison between (BIPP)TaCl3 (THF) (11)
where the BIPP ligand is bound cis-octahedral and (BIPP)-
TaBn3 (13) where the BIPP ligand is bound in diequatorial-
TBP positions shows that ethylene-linked phenoxides are
more flexible than anticipated. This flexibility appears to arise
(3-Isopropyl-2-methoxyphenyl)lithium‚0.5TMEDA (3). A 500
mL Schlenk flask equipped with a magnetic stir bar was charged
(23) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-SensitiVe
Compounds, 2nd ed.; John Wiley and Sons: New York, 1986.
Inorganic Chemistry, Vol. 43, No. 2, 2004 721

Anthis et al.
with 208 mL (0.333 mol) of 1.6 M n-butyllithium in hexanes. This
solution was stirred and cooled to 0 °C in an ice bath, after which
19.36 g (0.167 mol) of TMEDA was added dropwise via syringe
to yield a thick white suspension. The suspension was stirred at 0
°C for 1 min, after which 50.00 g (0.333 mol) of 2-isopropylanisole
(2) was added via syringe. After the addition of 2 was complete,
the mixture was allowed to warm to room temperature to afford a
clear, golden-yellow solution. This solution was stirred at room-
temperature overnight to yield a thick, white precipitate. The
precipitate was filtered off, washed with 50 mL of pentane, and
dried in vacuo to afford 54 g (0.252 mol, 76%) of 3 as a fine,
white powder. 1H NMR (C6D6): δ 8.08 (pseudo dd (ABC mult), 1
H, Haryl), 7.26 (pseudo t (ABC mult), 1 H, C(4)H, Haryl), 7.17
(pseudo dd (ABC mult), 1 H, Haryl), 3.31 and 3.28 (overlapped spt
and br s, respectively, 4 H total, CHMe2, ArOMe), 1.92 (s, 2 H,
Me2NCH2CH2NMe2), 1.83 (s, 6 H, Me2NCH2CH2NMe2), 1.24 (d,
6 H, CHMe2). 13C NMR (C6D6): δ 167.8, 163.3, 139.5, 136.5,
125.2, 125.1, 60.1, 57.5, 45.9, 27.3, and 24.2. Anal. Calcd for
C13H21NOLi (includes 0.5 TMEDA): C, 72.88; H, 9.88; N, 6.53.
Found: C, 72.61; H, 9.47; N, 5.88.
silica gel, and the reaction solids were washed with 2 × 50 mL of
a diethyl ether/pentane (1:2 v/v) mixture. The volatile components
were removed from the combined filtrate in vacuo to yield a pale
yellow oil. Distillation of this oil under reduced pressure provided
32.56 g (0.134 mol, 86%) of 5 as a clear colorless liquid with a
1
boiling point of 135-137 °C (13 mmHg). H NMR (C6D6): δ
6.98-7.03 (mult, 2 H, C(3)H and C(5)H, Haryl), 6.86 (pseudo t
(ABC mult), 1 H, C(4)H, Haryl), 4.33 (s, 2 H, ArCH2Br), 3.55 (s,
3 H, ArOMe), 3.23 (spt, 1 H, CHMe2), and 1.08 (d, 6 H, CHMe2).
13C (C6D6): δ 156.2, 142.4, 131.6, 129.3, 127.6, 124.9, 61.7, 28.6,
26.5, 23.8 (CHMe2). Anal. Calcd for C11H15OBr: C, 54.34; H, 6.21.
Found: C, 54.67; H, 6.24.
1,2-Bis(3-isopropyl-2-methoxyphenyl)ethane (Me2BIPP, 6). A
500 mL Schlenk flask equipped with a magnetic stir bar was
charged with a solution of 32.56 g (0.134 mol) of 5 in 100 mL of
THF/pentane (3:1 v/v). This solution was stirred and cooled to -100
°C (diethyl ether/liquid-N2 slush), and 84 mL (0.134 mol) of 1.6
M n-butyllithium in hexanes was slowly added over a period of
0.5 h to afford a white suspension. After the addition was complete,
the mixture was stirred at -100 °C for 1 h, allowed to warm to
-78 °C (diethyl ether/dry ice), and stirred at that temperature for
3 h. The resulting mixture was then carefully cannula-transferred
into a 500 mL separatory funnel containing 150 mL of water. The
organic layer was washed with water followed by 2 × 150 mL of
saturated aqueous NaCl and dried over anhydrous MgSO4. The
solution volatiles, after filtration, were evaporated under reduced
pressure to yield a pale yellow, viscous oil. Distillation of this oil
under reduced pressure provided 15.56 g (0.048 mol, 71%) of 6 as
2-(Hydroxymethyl)-6-isopropylanisole (4). A 500 mL, two-
neck round-bottom flask, equipped with a magnetic stir bar and a
nitrogen inlet adapter, was charged with a solution of 25.0 g (0.117
mol) of 3 in 250 mL of diethyl ether. A solid addition tube
containing 3.50 g (0.117 mol) of paraformaldehyde was attached
to the flask. The reaction mixture was cooled to 0 °C in an ice
bath, and the paraformaldehyde was added while the solution was
stirred. After addition was complete, the reaction was stirred for
another 10-15 h, while slowly warming to room temperature, over
which time a white solid precipitated. The mixture was carefully
hydrolyzed by adding 150 mL of 0.5 M aqueous HCl to the reaction
mixture with vigorous stirring, which caused the precipitate to
dissolve. The organic layer was separated, washed with 2 × 150
mL of saturated aqueous NaCl solution, dried over anhydrous
MgSO4, and filtered, and the reaction volatiles were removed in
vacuo to give a pale yellow oil. Distillation of this oil under reduced
pressure yielded 17.0 g (94.4 mmol, 80.6%) of 4 as a clear, colorless
oil with a boiling point of 119-121 °C (5 mmHg). 1H NMR
(C6D6): δ 7.21 (pseudo dd (ABC mult), 1 H, Haryl), 7.08 (pseudo
dd (ABC mult), 1 H, Haryl), 7.00 (pseudo t, (ABC mult), 1 H, C(4)H,
1
a colorless oil, bp 185-190 °C (10 mmHg). H NMR (C6D6): δ
7.17-7.02 (m, 6 H, Haryl), 3.47 (s, 6 H, OCH3), 3.41 (spt, 2 H,
CHMe2), 3.07 (s, 4 H, CH2CH2), 1.21 (d, 12 H, CHMe2). 13C NMR
(C6D6): δ 156.37, 142.07, 135.51, 128.50, 124.91, 124.76, 61.37,
32.20, 26.77, 25.15. Anal. Calcd for C22H30O2: C, 80.94; H, 9.26.
Found: C, 81.03; H, 9.69.
1,2-Bis(3-isopropyl-2-hydroxyphenyl)ethane (H2BIPP, 1). A
solution of 14.74 g (0.045 mol) of 6 in 250 mL of CH2Cl2 was
added to a Schlenk tube containing a magnetic stir bar. The solution
was stirred and cooled to -78 °C after which 90 mL (0.090 mol)
of a 1 M BBr3 solution in CH2Cl2 was slowly added. A white
precipitate formed as the BBr3 solution was added. The resulting
slurry was stirred overnight and allowed to slowly warm to room
temperature. The resulting brown-yellow solution was transferred
into a separatory funnel and carefully hydrolyzed with water, which
resulted in precipitation of a pale yellow solid. The solid was
redissolved by adding a minimal amount of Et2O. The organic layer
was separated, washed with 2 × 100 mL of saturated aqueous NaCl
solution, dried over anhydrous MgSO4, filtered, and evaporated in
vacuo to yield a brownish yellow oil. This oil was dissolved in 30
mL of pentane and filtered through a pad of alumina. The solvent
was evaporated from the filtrate in vacuo to give 11.74 g (0.039
Haryl), 4.62 (s, 2 H, ArCH2OH), 3.41 (s, 3 H, ArOMe), 3.31 (spt, 1
H, CHMe2), 2.20 (br s, 1 H, ArCH2OH), 1.16 (d, 6 H, CHMe2).
13C NMR (C6D6): δ 155.7, 141.8, 134.5, 126.8, 126.2, 124.8 (C(4),
Caryl), 61.7 (ArOCH3), 61.0 (ArCH2OH), 26.5 (CHMe2), 24.0
(CHMe2). Anal. Calcd for C11H16O2: C, 73.30; H, 8.94. Found:
C, 73.35; H, 8.68.
2-(Bromomethyl)-6-isopropylanisole (5). A 500 mL, three-neck
round-bottom flask equipped with a magnetic stir bar, nitrogen inlet
adapter, and a thermometer was charged with a solution of 83.3 g
(0.318 mol) of triphenylphosphine in 250 mL of CH2Cl2. The
reaction mixture was cooled to 0 °C in an ice bath and vigorously
stirred, while a solution of 51.05 g (0.313 mol) of Br2 in 50 mL of
CH2Cl2 was added dropwise at a sufficiently slow rate to maintain
the reaction temperature below 10 °C. A pale yellow solid
precipitated as the reaction proceeded. After the addition was
complete a solution of 28.31 g (0.151 mol) of 4 in 50 mL of CH2-
Cl2 was added, while maintaining the reaction temperature below
10 °C. After the addition was complete the reaction mixture was
allowed to warm to room temperature. After being stirred for 3 h,
the mixture was transferred into a 2 L Erlenmeyer flask, and 500
mL of diethyl ether was added followed by 1 L of pentane while
the reaction mixture was stirred vigorously with an overhead
mechanical stirrer. This mixture was then filtered through a pad of
1
mol, 87%) of 1 as a pale brown oil. H NMR (C6D6): δ 7.07-
6.86 (m, 6 H, Haryl), 5.58 (s, 2 H, OH), 2.95 (spt, 2 H, CHMe2),
2.81 (s, 4 H, CH2CH2), 1.16 (d, 12 H, CHMe2). 13C NMR (C6D6):
δ 151.42, 134.28, 127.78, 124.70, 121.22, 121.14, 32.60, 27.20,
22.86. Anal. Calcd for C20H26O2: C, 80.50; H, 8.78. Found: C,
80.16; H, 9.06.
(BIPP)TiCl2 (7). A solution of 0.639 g (3.37 mmol) of TiCl4 in
3 mL of pentane was prepared. A solution of 0.997 g (3.34 mmol)
of H2BIPP dissolved in 3 mL of pentane was prepared and was
added dropwise to the vigorously stirred TiCl4 solution. When the
evolution of gas was complete, the reaction mixture was allowed
to stir for another 4 h, after which time the reaction mixture was
cooled to -40 °C. After 10 days at this temperature, the resulting
722 Inorganic Chemistry, Vol. 43, No. 2, 2004

Chelating Bis(aryloxide) Ligands
solid which had precipitated was filtered off and dried in vacuo to
afford 1.20 g (2.90 mmol, 87%) of analytically pure product as a
dark red powder. H NMR (C6D6): δ 6.91-6.77 (m, 6 H, Haryl),
3.72 (spt, 2 H, CHMe2), 2.49 (s, 4 H, CH2CH2), 1.27 (d, 12 H,
CHMe2). 13C NMR (C6D6): δ 167.42 (Cipso), 131.17, 133.53 (Co),
127.38, 125.52 (Cm), 124.65 (Cp), 33.00 (CH2CH2), 28.49 (CHMe2),
22.90 (CHMe2). Anal. Calcd for C20H24Cl2O2Ti: C, 57.86; H, 5.83.
Found: C, 57.42; H, 6.11.
obtained by crystallization of the yellow product at -35 °C from
concentrated THF solutions.
1
The THF adduct (BIPP)TaCl3(THF) (11) was also prepared in
nearly quantitative yield (ca. 95%) by dissolving (BIPP)TaCl3 (10)
in neat THF, followed by removal of the solvent in vacuo to afford
yellow crystals. The NMR properties of this compound were
essentially identical with those of the base free (BIPP)TaCl3 in THF,
other than integration intensities. 1H NMR (THF-d8): δ 7.30-6.90
(m, 6 H, Haryl), 4.35 and 3.87 (spt, 1 H each, CHMe2), 3.6 (br, 4
H, HR THF), 2.90 (br, 4 H, CH2CH2), 1.7 (br, 4 H, Hâ THF), 1.30
(d, 12 H, CHMe2). Anal. Calcd for C28H40Cl3O4Ta (includes lattice
THF): C, 46.20; H, 5.54. Found: C, 46.34; H, 5.70.
(BIPP)TaCl3(Et2O) (12). A solution of 0.168 g (0.47 mmol) of
TaCl5 in 3 mL of diethyl ether was prepared and rapidly stirred
while a solution of 0.142 g (0.47 mmol) of H2BIPP in 3 mL of
diethyl ether was added over a 5 min period. The reaction was
allowed to stir for an additional 8 h, after which time the product
was precipitated with pentane. The resulting yellow powder was
filtered out, washed with pentane (3 × 5 mL), and dried in vacuo
to afford 0.265 g of 12 which contained a nonstoichometric amounts
of ether. This solvent could be substantially removed under high
vacuum over an extended period of time, such that the formulation
of 12 approached (BIPP)TaCl3(OEt2). Pure crystals which contained
one lattice ether molecule, (BIPP)TaCl3(OEt2)‚OEt2 (12‚OEt2), were
obtained by crystallization of the yellow product at -35 °C from
concentrated diethyl ether solutions.
(BIPP)TiMe2 (8). A solution of 0.25 g (0.61 mmol) of 7 in 2
mL of pentane was prepared. A 0.401 mL (1.20 mmol) portion of
3 M MeMgCl in THF was diluted to 1 mL in pentane and was
added dropwise to the rapidly stirring solution of 7. After being
stirred for 48 h at room temperature, the reaction mixture was
filtered through Celite, and the resulting yellow filtrate was cooled
to -40 °C. After 5 h at -40 °C, 0.08 g (0.21 mmol, 36%) of
analytically pure red crystals had formed, which was collected and
dried in vacuo. 1H NMR (C6D6): δ 7.13-6.92 (m, 6 H, Haryl), 4.10
(spt, 2 H, CHMe2), 2.31 (s, 4 H, CH2CH2), 1.48 (d, 12 H, CHMe2),
1.33 (TiCH3). Anal. Calcd for C22H30O2Ti: C, 70.59; H, 8.08.
Found: C, 70.21; H, 8.02
(BIPP)Ti(CH2C6H5)2 (9). A solution of 0.30 g (0.73 mmol) of
7 in 5 mL of Et2O was prepared. A 1.44 mL (1.44 mmol) sample
of 1 M (CH2C6H5)MgCl in THF was diluted to 3 mL with Et2O
and added dropwise to the vigorously stirred solution of 7. After
being stirred for 20 h at room temperature, the solution was filtered
through Celite, and the solvent was removed from the filtrate in
vacuo to afford a red oil. This oil was triturated with pentane to
afford an orange solid, which was filtered off and dried in vacuo
giving 0.186 g (0.35 mmol, 49%) of 9 as a red orange powder. 1H
NMR (C6D6): δ 7.12-6.76 (m, 16 H, Haryl), 3.88 (spt, 2 H,
CHMe2), 2.80 (s, 4 H, CH2CH2), 2.17 (CH2C6H5), 1.42 (d, 12 H,
The Et2O adduct (BIPP)TaCl3(Et2O) (12) was also prepared in
nearly quantitative yield (ca. 95%) by dissolving (BIPP)TaCl3 (10)
in neat Et2O, followed by removal of the solvent in vacuo to afford
1
yellow crystals. H NMR (C6D6, 70 °C): δ 7.13-6.84 (m, 6 H,
H
aryl), 4.19 (br s, 6 H, CHMe2 and MeCH2O), 2.93 (br s, 4 H, CH2-
CH2), 1.31 (br d, 12 H, CHMe2), 1.05 (t, 6 H, MeCH2O). 13C NMR
(C6D6 70°C): δ 159.00 (Cipso), 141.78 (Co), 135.42 (Co), 127.12
(Cm), 125.93 (Cp), 124.82 (Cm), 69.49 (CH2O, ether), 34.42 (CH2-
CH2), 26.54 (CHMe2), 24.32 (CHMe2), 12.50 (CH3, ether). Anal.
Calcd for C28H44Cl3O4Ta (includes lattice Et2O): C, 45.95; H, 6.06;
Cl, 14.53. Found: C, 46.06; H, 5.44; Cl, 14.01.
CHMe2). 13C NMR (C6D6): δ 162.16 (Cipso, BIPP), 141.91 (Cipso
,
benzyl), 136.15, 132.90 (Co, BIPP), 129.35, 128.78 (Co, Cm,
Benzyl), 127.61 (Cp, benzyl), 124.46, 124.25 (Cm, BIPP), 122.63
(Cp, BIPP), 81.69 (CH2C6H5), 33.04 (CHMe2), 27.62(CH2CH2),
23.59 (CHMe2). Anal. Calcd for C23H38O2Ti: C, 77.56; H, 7.27.
Found: C, 76.82; H, 7.66.
(BIPP)Ta(CH2C6H5)3 (13). A solution of 0.253 g (0.43 mmol)
of (BIPP)TaCl3 (10) in 8 mL of Et2O was prepared. A 1.28 mL
(1.28 mmol) sample of 1 M (CH2C6H5)MgCl in THF was diluted
to 5 mL with Et2O and was added dropwise to the stirred solution
of 10. After being stirred for 16 h, the solution was filtered through
Celite, and the solvent was removed from the filtrate in vacuo. The
residue was extracted with pentane, and the extract was filtered
through Celite. The filtrate was cooled to -40 °C to afford 0.125
(BIPP)TaCl3 (10). A suspension of 4.11 g (11.5 mmol) of TaCl5
in 25 mL of benzene was prepared and vigorously stirred. A solution
of 3.45 g (11.5 mmol) of H2BIPP dissolved in 25 mL of benzene
was slowly added (over ca. 5 min) to the stirred TaCl5 suspension.
The evolution of gas was observed, after which time the reaction
was stirred at room temperature for an additional 4 days. After
this time, the precipitate which had formed was filtered off and
dried in vacuo to give 5.68 g (9.73 mmol, 85%) of product 10 as
1
g (0.17 mmol, 39%) of 13 as X-ray-quality orange crystals. H
1
a yellow solid. H NMR (THF-d8): δ 7.28-6.90 (m, 6 H, Haryl),
NMR (C6D6): δ 7.09-6.65 (m, 21 H, Haryl), 3.51 (spt, 2 H,
CHMe2), 3.40 (s, 4 H, CH2CH2), 1.38 (s, 6 H, CH2C6H5), 1.29 (d,
12 H, CHMe2). 13C NMR (C6D6): δ 157.94 (Cipso, BIPP), 145.77
(Cipso, benzyl), 137.79, 131.13 (Co, BIPP), 129.21, 128.15 (Co, Cm,
benzyl), 127.37 (Cp, benzyl), 124.45, 124.11 (Cm, BIPP), 123.98
(Cp, BIPP), 80.7 (CH2C6H5), 30.57 (CHMe2), 27.31 (CH2CH2),
23.22 (CHMe2). Anal. Calcd for C41H45O2Ta: C, 65.59; H, 6.04.
Found: C, 65.05; H, 5.96.
(BIPP)TaMe3 (14). A solution of 0.247 g (0.42 mmol) of
(BIPP)TaCl3 (10) in 10 mL of Et2O was prepared. A 0.428 mL
(1.28 mmol) sample of 3 M MeMgCl in THF was diluted to 5 mL
with Et2O and added dropwise to the vigorously stirred solution of
10. After being stirred for 18 h, the reaction mixture was filtered
through Celite and the solvent was removed from the filtrate in
vacuo. The residue was extracted with pentane and filtered through
Celite. The resulting filtrate was cooled to -40 °C. After ca. 24 h
at this temperature, 0.073 g of a pale yellow powder had precipitated
4.35 and 3.87 (spt, 1 H each, CHMe2), 3.58 (br s, THF), 2.90 (br
s, 4 H, CH2CH2), 1.73 (br s, THF), 1.30 (d, 12 H, CHMe2). Anal.
Calcd for C20H24Cl3O2Ta: C, 41.15; H, 4.14. Found: C, 41.29; H,
4.11.
(BIPP)TaCl3(THF) (11). A solution of 0.198 g (0.55 mmol) of
TaCl5 in 3 mL of THF was prepared and rapidly stirred while a
solution of 0.165 g (0.55 mmol) of H2BIPP in 3 mL of THF was
added over about a 5 min period. The reaction was allowed to stir
for an additional 8 h, after which time the product was precipitated
with pentane. The resulting yellow powder was filtered off, washed
with pentane (3 × 5 mL), and dried in vacuo to afford 0.302 g
(83%) of 11 which contained a nonstoichometric amounts of THF.
This solvent could be substantially removed under high vacuum
over an extended period of time, such that the formulation of 11
approached (BIPP)TaCl3(THF). Pure crystals which contained one
lattice THF molecule, (BIPP)TaCl3(THF)‚THF (11‚THF), were
Inorganic Chemistry, Vol. 43, No. 2, 2004 723

Anthis et al.
a mixture of products which could not be separated further. The
major product via NMR (∼80%) is consistent with the structure of
14. 1H NMR (C6D6): δ 7.13-6.84 (m, 6 H, Haryl), 3.81 (spt, 2 H,
CHMe2), 2.63 (s, 4 H, CH2CH2), 1.40 (s, 9 H, TaMe3), 1.26 (d, 12
H, CHMe2). 13C NMR (C6D6): δ 157.45 (Cipso), 139.69, 131.78
(Co), 126.98, 125.13, 124.45 (Cm, Cp), 65.09 (TaMe), 33.84
(CHMe2), 27.00 (CH2CH2), 23.71 (CHMe2).
X-ray Structural Determination of (BIPP)Ta(CH2C6H5)3
(13). A orange diamond shaped block of C41H45O2Ta was
crystallized from Et2O solution at -35 °C and was mounted
on a glass fiber in a random orientation. The crystal was
examined using a Bruker AXS SMART 1000 CCD detector
X-ray diffractometer, and raw data were solved using the
Bruker SHELXTL software package.20 Systematic absences
and intensity statistics indicate the space group to be P21/c
(No. 14), which was consistent with refinement. Hydrogen
atoms were added at idealized positions, constrained to ride
on the atom to which they are bonded, and given thermal
parameters equal to 1.2 or 1.5 times Uiso of that bonded atom.
Scattering factors and anomalous dispersion were taken from
the International Tables Vol. C, Tables 4.2.6.8 and 6.1.1.4.
Details of the structural determination and refinement are
reported in Table 1.
Crystallography
X-ray Structural Determination of (BIPP)TaCl3(THF)‚
THF (11‚THF). A yellow cube crystal of C28H40Cl3O4Ta
was crystallized from THF solution at -35 °C and was
mounted on a glass fiber in a random orientation. Examina-
tion of the crystal on a Bruker AXS SMART 1000 CCD
detector X-ray diffractometer revealed the crystal to be a
pseudomirrorhedral twin. The initial data set of 78 412
reflections (26 397 unique) was separated into three data sets
(A, B, and overlapping) using the “twin” software package
(Bruker SHELXTL software package).20 The two indepen-
dent data sets were then solved and merged using a BASF
parameter of 0.64210. Systematic absences and intensity
statistics indicated the space group to be P21/c (No. 14),
which was consistent with refinement. Hydrogen atoms were
added at idealized positions, constrained to ride on the atom
to which they are bonded, and given thermal parameters
equal to 1.2 or 1.5 times Uiso of that bonded atom. Scattering
factors and anomalous dispersion were taken from the
International Tables Vol. C, Tables 4.2.6.8 and 6.1.1.4.
Details of the structural determination and refinement are
reported in Table 1.
Acknowledgment is made to the National Science Foun-
dation (Grant CHE-9730000) for support of this research.
Molecular structures were determined at the Molecular
Structure Laboratory, University of Arizona, through the
assistance of the National Science Foundation (Grant
CHE9610374). We thank Dr. Michael Carducci for sharing
his invaluable crystallographic expertise in solving the crystal
structures reported herein.
Supporting Information Available: Complete crystallographic
details in CIF format. This material is available free of charge via
the Internet at http://pubs.acs.org.
IC030300S
724 Inorganic Chemistry, Vol. 43, No. 2, 2004